1. Field of the Invention
This invention relates to vehicular automatic and semi-automatic mechanical transmission systems and, in particular, to at least partially automatic mechanical transmission systems of the type providing at least partially automatic implementation of selected changes or shifting of mechanical transmission gear ratios including sensing of non-torque lock conditions prior to attempting to disengage an existing ratio to minimize wear and damage to the actuators, shift forks and/or jaw clutch members.
2. Description of the Prior Art
Fully automatic transmission systems, both for heavy-duty vehicles such as heavy-duty trucks, and for automobiles, that sense throttle openings or positions, vehicle speeds, engine speeds, and the like, and automatically shift the vehicle transmission in accordance therewith, are well known in the prior art. Such fully automatic change gear transmission systems include automated transmissions wherein pressurized fluid is utilized to frictionally engage one or more members to other members or to a ground to achieve a selected gear ratio as well as automated mechanical transmissions utilizing electronic and/or pneumatic logic and actuators to engage and disengage mechanical (i.e. positive) clutches to achieve a desired gear ratio. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,961,546; 4,081,065 and 4,361,060, the disclosures of which are hereby incorporated by reference.
Semi-automatic transmission systems utilizing electronic control units which sense throttle position, engine, input shaft, output shaft and/or vehicle speed, and utilize automatically controlled fuel throttle devices, gear shifting devices and/or master clutch operating devices to substantially fully automatically implement operator manually selected transmission ratio changes are known in the prior art. Examples of such semi-automatic transmission systems may be seen by reference to U.S. Pat. Nos. 4,425,620; 4,631,679 and 4,648,290, the disclosures of which are incorporated herein by reference.
The prior art automatic/semi-automatic transmission systems may be too expensive for certain applications as a relatively large number of sensors and automatically controllable actuators, such as a master clutch and/or a fuel throttle device actuator, are required to be provided, installed and maintained and/or if not provided with clutch and/or fuel throttle actuators tended to command disengagement of existing ratios under torque lock conditions which resulted in unacceptably high wear of the actuator, shift forks and/or jaw clutches.